Commercial transport aircraft fuselage and wing structures may be built by assembling stiffened panels, for example fuselage skin panels with frames and stringers or wing skin panels with ribs and stringers, by means of mechanically fastened joints. For example, fuselage stiffened panels may be assembled in single lab shear-joints longitudinally, i.e. in flight direction, to form a fuselage barrel which may be assembled together with the next fuselage barrel by means of circumferential joints, which may be in a butt-joint configuration. Moreover, wing box structures may be assembled in similar fashion by means of butt-joints, for example cordwise and spanwise.
Due to the cyclic loads that affect aircraft structures are subjected, fatigue crack initiation and growth may affect the aircraft structures. Among others, locations that are prone to fatigue damages are the mechanically fastened joints such as longitudinal and circumferential joints in fuselage or in wing structures. Usually, such cracks propagate longitudinally and circumferentially on the fuselage or cordwise on wing panels. In order to prevent this, the fuselage of the aircraft has to be regularly maintained and inspected.
Nowadays, doublers or straps made of titanium alloys may be used as selective reinforcement structure to slow down crack growth and to eventually stop the propagation and to ensure large damage capability. A commonly adapted solution relates to the use of crack stoppers which are, for example, made of titanium. Such stiffeners or crack stoppers are currently applied to longitudinal frames of fuselage structures.
DE 10 2012 111 022 relates to a vehicle structure component reinforced by means of an area comprising compressive residual stresses in a first direction and compressive or tensile residual stresses in a second direction.
DE 10 2008 044 407 relates to a method for preventing crack formation and for slowing down the advancement of a crack in metal aircraft structures by way of laser shock rays.